Considerations for scaling to millions of users
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Questions and Answers

What is the first step in designing a system that supports millions of users?

  • Building a complex system from the beginning
  • Purchasing a domain name and hosting DNS services on our servers
  • Setting up a single server to run everything initially (correct)
  • Configuring multiple servers to handle different tasks

    • Which component is typically not hosted by the system’s servers when users access websites through domain names?

  • Domain Name System (DNS) (correct)
  • HTML pages or JSON response
  • Hypertext Transfer Protocol (HTTP)
  • Internet Protocol (IP) address

    • What protocol are HTTP requests sent through to the web server?

  • Domain Name System (DNS)
  • Hypertext Transfer Protocol (HTTP) (correct)
  • Internet Protocol (IP)
  • Transmission Control Protocol (TCP)

    • What is the purpose of the single server setup illustrated in Figure 1?

    <p>To illustrate running everything on a single server initially</p> Signup and view all the answers

    What is the primary benefit of database replication for system performance?

    <p>Improved parallel processing of read operations</p> Signup and view all the answers

    In the event of a database failure, how can the system handle the situation?

    <p>Promoting a slave database to be the new master</p> Signup and view all the answers

    What is the purpose of a cache in a system architecture?

    <p>To improve system performance by storing data for faster access</p> Signup and view all the answers

    What should be considered when deciding to use a cache in a system?

    <p>Frequency of data reads and modifications</p> Signup and view all the answers

    How can cached data be prevented from becoming stale?

    <p>By implementing an expiration policy for cached data</p> Signup and view all the answers

    What is the purpose of keeping the data store and the cache in sync?

    <p>To avoid inconsistencies and data loss</p> Signup and view all the answers

    Why is it advisable to use multiple cache servers across different data centers?

    <p>To maintain system availability and avoid a single point of failure</p> Signup and view all the answers

    What is the purpose of overprovisioning cache servers?

    <p>To ensure sufficient memory is available and handle increased traffic</p> Signup and view all the answers

    What is the purpose of a content delivery network (CDN)?

    <p>To deliver static content using a network of geographically distributed servers</p> Signup and view all the answers

    Which caching policies are commonly used in cache eviction?

    <p>LRU, LFU, and FIFO</p> Signup and view all the answers

    What does a stateful server do compared to a stateless server?

    <p>Remembers client data from one request to the next</p> Signup and view all the answers

    Why is setting an appropriate cache expiry time important in a CDN?

    <p>To ensure fresh content delivery</p> Signup and view all the answers

    What is the purpose of moving state data out of the web tier in a stateless web tier architecture?

    <p>To scale the web tier horizontally</p> Signup and view all the answers

    How does a CDN workflow function when a user visits a website?

    <p>A CDN server closest to the user delivers static content; if not available, it requests the file from the origin and caches it.</p> Signup and view all the answers

    What is the benefit of fetching static assets from a CDN instead of web servers?

    <p>Better performance and lightened database load</p> Signup and view all the answers

    What is the primary function of a load balancer in a web server environment?

    <p>Improving performance by evenly distributing incoming traffic</p> Signup and view all the answers

    What type of databases are suitable for low latency, unstructured data, and large data sets?

    <p>Graph stores</p> Signup and view all the answers

    Which method is better for handling high traffic in large scale applications?

    <p>Horizontal scaling</p> Signup and view all the answers

    What is the primary benefit of separating web/mobile traffic and database servers?

    <p>Allowing independent scaling of servers</p> Signup and view all the answers

    In a master/slave relationship, what is the role of slave databases in database replication?

    <p>They serve as read-only databases to improve performance and availability</p> Signup and view all the answers

    Which feature makes non-relational databases suitable for serialization/deserialization requirements?

    <p>Handling unstructured data efficiently</p> Signup and view all the answers

    What is the main advantage of using vertical scaling for low traffic scenarios?

    <p>Simple solution without the need for additional servers</p> Signup and view all the answers

    What communication protocol does the mobile application use to interact with the web server?

    <p>HTTP</p> Signup and view all the answers

    Which type of databases are suitable for join operations using SQL?

    <p>Relational databases</p> Signup and view all the answers

    What is the main purpose of using database replication in a system?

    <p>Providing redundancy and failover capabilities</p> Signup and view all the answers

    What is the primary function of a relational database?

    <p>Storing data in tables, rows, and supporting join operations using SQL</p> Signup and view all the answers

    What is the key benefit of using non-relational databases for large data sets?

    <p>Efficient handling of unstructured data</p> Signup and view all the answers

    What is the primary purpose of GeoDNS in a multi-data center setup?

    <p>To distribute traffic to the closest data center and split traffic between data centers</p> Signup and view all the answers

    What is the purpose of message queues in a system with independent scaling?

    <p>To serve as a buffer for distributing asynchronous requests between producers and consumers</p> Signup and view all the answers

    What is the primary benefit of database replication for system performance?

    <p>To keep data consistent and improve fault tolerance</p> Signup and view all the answers

    What is the purpose of horizontal database scaling?

    <p>To store and handle large amounts of data using powerful database servers</p> Signup and view all the answers

    What protocol are HTTP requests sent through to the web server?

    <p>TCP/IP</p> Signup and view all the answers

    What is the purpose of a cache in a system architecture?

    <p>To temporarily store frequently accessed data for faster retrieval</p> Signup and view all the answers

    Why is it advisable to use multiple cache servers across different data centers?

    <p>To avoid overloading a single cache server and improve fault tolerance</p> Signup and view all the answers

    In the event of a database failure, how can the system handle the situation?

    <p>By directing all traffic to a healthy data center</p> Signup and view all the answers

    What should be considered when deciding to use a cache in a system?

    <p>Scalability, fault tolerance, and eviction policies for cache management</p> Signup and view all the answers

    What is the purpose of overprovisioning cache servers?

    <p>To avoid overloading a single cache server and improve fault tolerance</p> Signup and view all the answers

    What is the first step in designing a system that supports millions of users?

    <p>Solve challenges like traffic redirection using GeoDNS and data synchronization across multiple data centers.</p> Signup and view all the answers

    Study Notes

    • Database replication improves system performance by allowing read operations to be processed in parallel across multiple servers (slave nodes), while writes and updates are processed in master nodes.

    • Replication improves system reliability by preserving data across multiple locations, preventing data loss in the event of a natural disaster or server failure.

    • In case of a database failure, the system can handle the situation by redirecting read operations to available slave databases or promoting a healthy slave database to be the new master.

    • A cache is a temporary storage area that stores the result of expensive responses or frequently accessed data in memory for faster access, reducing the load on the database and improving system performance.

    • Cache servers provide APIs for common programming languages, making it simple to interact with them.

    • Decide when to use a cache based on data access patterns: use it when data is read frequently but modified infrequently, and save important data in persistent data stores.

    • Implement an expiration policy for cached data to prevent it from being stored in volatile memory indefinitely and becoming stale.

    • Keep the data store and the cache in sync to avoid inconsistencies.

    • Use multiple cache servers across different data centers to avoid a single point of failure and maintain system availability.

    • Overprovision cache servers by certain percentages to handle increased traffic and ensure sufficient memory is available.

    • After removing state data from web servers, auto-scaling of web tier is achieved by adding or removing servers based on traffic load.

    • Geo-routed traffic to closest data center using GeoDNS in normal operation, split traffic between data centers.

    • In the event of a data center outage, all traffic is directed to a healthy data center.

    • Multi-data center setup requires solving challenges like traffic redirection (using GeoDNS) and data synchronization (replicating data across multiple data centers).

    • Decoupling different components of the system through message queues for independent scaling.

    • Message queues serve as a buffer distributing asynchronous requests with producers and consumers interacting asynchronously.

    • Logging, monitoring, metrics, and automation are essential for large-scale websites for error identification, business insights, and system health.

    • Database scaling approaches include vertical scaling (adding more power to existing machine) and horizontal scaling (adding more machines).

    • Vertical scaling can store and handle large amounts of data using powerful database servers.

    • Database servers can be extremely powerful, Amazon RDS offers a server with 24 TB of RAM.

    • stackoverflow.com in 2013 had over 10 million monthly users, demonstrating the scale that can be achieved with powerful database servers.

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    Description

    Learn about the advantages of database replication, such as improved performance and increased reliability. Explore how the master-slave model distributes read and write operations, enhancing parallel query processing and preserving data in case of server destruction.

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